The present invention is specific to a process of electrospinning polytetrafluoroethylene (PTFE). More particularly, the present invention is related to electrospinning high viscosity PTFE dispersions and products manufactured thereby.
The process of electrostatic spinning is well known in the art as represented in U.S. Pat. Nos. 2,158,416; 4,043,331; 4,143,196; 4,287,139; 4,432,916; 4,689,186; 6,641,773 and 6,743; 273 each of which is incorporated herein by reference thereto. U.S. Pat. Nos. 4,323,525, 4,127,706 and 4,044,404, all of which are incorporated herein by reference, provide information related to processing and electrostatic spinning of PTFE from an aqueous or other dispersion.
Electrostatic spinning, also referred to in the art as electrospinning, involves a charged polymer moving towards a charged surface. In one embodiment the polymer is discharged through a small charged orifice, such as a needle, towards a target wherein the needle and target have opposing electrical charge. As would be realized, the nature of the polymer is critical. It has long been considered necessary in the art to maintain a relatively low viscosity of less than about 150 poise with viscosity being relatively higher for lower molecular weight polymers and relatively lower for higher molecular weight polymers. If the combination of viscosity and molecular weight were too high the fiberization was considered to be inadequate.
It has long been considered undesirable to increase the viscosity of the polymer solution over about 150 poise due to thixotropic limitations which cause orifice clogging, poor fiber formation, and the like. Furthermore, when a charged orifice is used the polymer fibers repel during flight which has long been believed to limit the number of fibers within a given volume of spray. Through diligent research the present inventors have determined, contrary to prior understandings, that a significant increase in viscosity to well above that previously considered feasible, actually improves the resulting material and provides additional properties and advantages not previously considered possible.